The present invention relates generally to radioactive sources used in the irradiation of body tissue. More particularly, the invention resides in devices, apparatus, and processes for relatively short term delivery of a radioactive source into the body of a cancer patient to expose the malignant tumor(s) to localized in vivo radiation from within through a catheter which terminates at or beyond the tumor site.
Radiation treatment of malignant tumors is one of the three traditional methods of treating cancer, the other two being surgery and chemotherapy. One technique for radiation treatment involves directing a beam of radiation from a point external to the patient's body onto the area of the body in which the tumor is located. The purpose of such treatment is to shrink and ultimately destroy the tumor, but since the treatment is not particularly selective except in a very gross sense, in delivering the treatment healthy tissue is also exposed to the high dosage of radiation in the beam and is therefore subject to injury. Another technique for radiation treatment involves the delivery of a highly radioactive source into the body directly to the tumor site for localized irradiation, for the same purpose as the external beam radiation technique, except that in this treatment exposure and injury to healthy tissue can be avoided to a considerably greater extent than with the external beam radiation.
A conventional localized low level radiation procedure involves the use of radioactive sources or "seeds" having activity levels on the order of one millicurie per source or seed. Typically, the seeds are implanted in either of two ways. They may be injected directly into the tumor site after surgically opening the patient, the incision then sutured to close the patient, with the intention that the radioactive seeds will be left permanently in place.
A second technique is to implant one or more catheters in the patient's body to extend through the tumor site, then insert a tube containing the radioactive sources or seeds through one of the catheters into the region of the tumor where the tube is left in place for the predetermined period of treatment, and repeat the procedure for each of the other catheters. The low level seeds expose the tumor to gamma rays during the period they are left in place. While undergoing such treatment the patient remains ambulatory, but among the disadvantages of such procedures, in addition to the requirement of surgical implantation, the patient must remain in the hospital during the entire treatment phase which is usually several days, during which time all personnel working with the patient are exposed to radiation.
Another method of localized internal radiation treatment of deep tumors also involves implanting one or more catheters to provide a path from a point external to the patient's body to and through the tumor site, to provide accessibility to the interior of the tumor mass via the catheter(s). A highly radioactive source, typically having an intensity of ten curies, is then mechanically delivered on a retractable guide wire through the catheter for localized irradiation of the tumor for a very short period, usually in the range of only seconds up to a few minutes per treatment.
The high dose source is secured to the distal or remote end of the guide wire, and is advanced or retracted through an attachment of the proximal or near end of the guide wire to the loader machine, by appropriate manipulation of controls by the attending technician or physician from the control panel of a console for actuating the apparatus. The loader is located in a remote radiation shielded room into which the patient is moved for the treatment. The source wire is advanced through the catheter to the proper location for treatment of the tumor, based on measurement of the extent of advancement of a previously positioned dummy wire having an opaque tip marker for fluoroscopic observation. The dummy wire is retracted prior to moving the patient into the shielded room for the actual treatment.
In the case of an abdominal tumor, for example, an incision is made in the patient to open the abdominal cavity, and a needle is inserted into and through the tumor to provide a desired number of entries. A separate catheter is then implanted in each passageway formed by the needle, of sufficient length to be accessible from a point external to the body after the patient is closed. For purposes of determining or verifying the point to which the radioactive source wire must be advanced into the catheter for the treatment, a dummy wire is manually inserted into the catheter by the physician until the opaquely marked tip of the distal end is properly positioned as viewed under fluoroscope.
After this procedure is repeated for each catheter and the results are recorded, the patient is moved into the shielded treatment room, which is provided with apparatus to permit television viewing from outside, and the patient is hooked up to the loading machine. Using the controls on the console panel, the source wire is driven by the loader to the recorded (programmed) depth into the respective catheter, for example 100 cm. The source wire is left in place in that position for the time interval required for the treatment (which is also programmed into the loader). The source wire is then automatically retracted by the loader and returned to a shielded storage area within the loader.
If several catheters are implanted through the tumor site or region, the loader repeats the process automatically for each one. The source wire is driven into the first channel (catheter), the period of treatment is performed, the source wire is then withdrawn, a wheel on the loader turns automatically to the position for insertion of the source wire into the next channel, whereupon it is advanced through the new catheter to the proper depth and is retracted after the treatment interval, and so forth.
For treatments conducted on an outpatient basis, the catheters are left in place and the patient comes in for the procedure as scheduled. This is described in co-pending patent application Ser. No. 07/255,045, filed Oct. 7, 1988. Where the geometries of the catheters are fixed, as by the technique disclosed in that application, it is unnecessary to re-implant the catheters daily (or on other periodic bases, according to the treatment regimen), which serves to spare the patient from the considerable trauma of more surgery. This is particularly important for a patient experiencing life-threatening illness, and the resulting psychological effect. It is only necessary to verify by fluoroscopy that the catheters have not been dislodged, and if that is the case, a treatment card previously produced for that particular patient is simply inserted into the loader, to cause the loader to go through an automatic repetition of the treatment according to the prescribed regime.
The treatment regime may be repeated at regular short intervals over the entire period of time that the patient requires treatment to shrink and ultimately eliminate the tumor. Among the advantages of this type of radiation therapy are exposure of the tumor to fractionated treatment doses of localized radiation so that each individual treatment need only be of extremely short duration to provide the desired effect while reducing the magnitude of patient discomfort, and to provide more rapid shrinking of the tumor while avoiding prolonged exposure of healthy tissue to the radiation.
The loader has many additional functions but the foregoing description of its operation is sufficient for present purposes. In essence, the machine serves to move the highly radioactive source into the patient a precise distance for treatment of the cancerous mass, and then retracts the source. If the source wire encounters a kink or other barrier to its advancement along the catheter path, the feed mechanism of the loader is designed to slip, and upon detection of such slippage, to reverse the drive for retraction of the source wire into the shielded storage safe. An error flag is then displayed to the operator at the console panel, together with information that the source wire cannot be advanced into the particular catheter beyond the specified distance (at which the kink or other barrier was encountered).
Because the malignancy may be located deep within the body, and its nature and extent may make it inoperable, it may be extremely difficult to reach by use of the source wire as the latter is guided through the path provided by the implanted catheter. It may be necessary as a practical matter that the catheter take a long and tortuous route to the site of the cancer, with numerous sharp bends and turns as well as longer and narrower passages. It is essential, therefore, that the source wire should be extremely thin, small diameter and flexible, and yet sufficiently strong to traverse such a path and reach the cancer site without breakage or significant delay, and that it be retractable in the same fashion.
It is a principal object of the present invention to provide a new and improved radioactive source wire which possesses those desirable characteristics and features.
A feature of the present invention is the provision of a design which enables the source wire to be maneuvered through tight turns, even kinks, so that treatment may be rendered as scheduled without need for additional procedures to allow advancement to the tumor site.
One of the more serious problems encountered in the use of hot (radioactive) cores capable of delivering high dosage radiation to the tumor site by means of remotely activated electromechanical loader, is that the hot core is rigid and relatively brittle. A suitable core, for example, is composed of substantially pure iridium (although other conventional source materials such as cobalt, cesium, palladium, iodine and so forth may be used instead), which can be irradiated to a relatively high level of radioactivity in a rather small size. Ir-192, produced in a nuclear reactor with dosages of up to 10 curies in a diameter that results in a source wire diameter of about 1.1 millimeters (mm) is typical of the prior art. Unless the core is adequately protected and packaged it may scale, flake or even fracture when in use. The brittleness of the core tends to cause flaking during mere handling, which increases the order of difficulty of forming the source wire. If radioactive flakes are deposited on the wire or other surfaces in which the core comes into contact, the result is undesirable contamination.
Also, the method of attaching the core to the guide-wire becomes critically important to assure its retention while the wire is being advanced into or withdrawn from the catheter, particularly in regions where binding may occur because of kinks and tight turns in the catheter. In one conventional prior art assembly the core is placed inside a stainless steel capsule with an open end on one side and welded to the delivery wire or guide wire. This technique suffers not only the disadvantage of increased flaking of the core material, but unless the weld is virtually perfect, can result in the presence of a dangerously weak spot at the point of the weld. Such weakness can result in fracture of the connection and separation of the core from the delivery wire in use, which would require emergency measures to be taken for its removal from the patient's body. Moreover, attempts to reduce the source and wire size, by reducing the respective outside diameter, only result in a decrease of the surface area to be welded, thereby further weakening the weld location.
A further object of the present invention is to provide a source wire for in vivo localized radioactive treatment of malignant tumors, in which the source wire components require no critical welds for their retention in the wire.
The rigidity of the typical hot core exacerbates the relatively unyielding nature of prior art source wires to tight turns in the catheter as the source wire is advanced or withdrawn therethrough. Beyond the possibility of breakage of the source wire from binding in the catheter, the surrounding tissue at the point of the binding is exposed to the high dosage of radiation for the duration of the time interval required to free the source wire, and the source wire may be prevented from being advanced fully to the tumor site.
Another object of the present invention is to provide an improved source wire which avoids such difficulties.
In my co-pending U.S. patent application Ser. No. 07/228,400, filed Aug. 4, 1988, there is disclosed a method of producing an ultra-thin iridium source wire of less than about 0.6 to 0.7 mm in diameter, by imbedding a smaller diameter core of substantially pure iridium in a hole drilled (e.g., by use of a laser) in a platinum wire of somewhat larger diameter than is ultimately desired, and then drawing the wire down to the smaller sized diameter. The platinum wire is reasonably strong and flexible, and despite the rigidity of the iridium core is capable of being maneuvered over relatively long passages through an implanted catheter, using remote afterloader equipment.
After assembly, the overall substantially unitary source wire of the 228,400 application is irradiated in a nuclear reactor to provide the iridium core with the desired high dosage of radiation (depending on size of the iridium core) appropriate for delivery to the tumor site within the body. The small diameter of this source wire allows the use of a commensurately small diameter catheter. A preferred embodiment of that source wire system is a substantially pure iridium fiber core approximately one cm in length and about 0.2 mm diameter, disposed one mm from the distal end of the platinum delivery wire which is about two meters long. In practice, this source wire is advanced, positioned and retracted using a remote afterloader of the type disclosed in co-pending U.S. application Ser. No. 255,044, filed Oct. 7, 1988 in the names of Spako et al. and titled "Apparatus and Method for the Remote Treatment of Cancer Using High Radioactivity Sources."
Despite the important advantages of such apparatus and methods for in vivo radiotherapy of malignant tumors, there are certain problems which remain to be addressed and resolved. A problem encountered with a highly radioactive core (high dose) source wire employing the principles of the invention disclosed in the 228,400 application is that the platinum becomes radioactive and is unusable for a period of several weeks (approximately ten platinum half-lives). In the meantime, the radioactivity of the core partially leaks away. The platinum wire and the cold iridium core imbedded in it are irradiated together in a nuclear reactor. The differential in the half-lives of the irradiated iridium and the irradiated platinum is important to the capability of the completed source wire to perform properly, but while the radioactive core becomes heavily radioactive, the platinum wire becomes slightly radioactive over a period of time and causes undesirable contamination.
It is another important object of the present invention to provide an improved design and method of fabrication for a high dose source wire.
A low dosage, hand loaded source wire having a platinum wire and iridium core is useful, because the cold core is readily encapsulated in platinum in long length on a spool, and the entire spool of wire may then be irradiated in a reactor. However, this source wire is of such low dose (typically, 0.4 to 25 milligram radium equivalent per cm, a standard unit of measure for radioactive strength) that the platinum contamination is insignificant. It is when the dosage exceeds one curie that the platinum contamination can become significant. In the low dose version, platinum is non-corrosive and will not oxidize in the presence of the radioactive core. The wire may be unspooled, cut into the length desired for treatment, and is self-sealing, as described in my co-pending patent application Ser. No. 07/061,468, filed Jun. 15, 1987.
It is a further object of the present invention to provide a low dose radioactive source wire having an improved design and method of fabrication, and which is readily usable in conjunction with a miniaturized source loader apparatus, or mini-loader, of the type previously described herein.
Yet another broad object of the present invention is to provide improvements in radioactive source wires and methods of manufacture thereof, to overcome the disadvantages found in prior art source wires.